This project is part of a continuing program to develop the use of quantitative affinity chromatography for the characterization of macromolecular interactions. As part of the current studies, adsorbents containing immobilized neuropeptide hormones and their analogues are being used to elucidate the binding interactions and ligand-induced self-association of bovine neurophysins (NP's). The quantitative chromatographic behavior observed with native NPII, and NPII, mononitrated at Tyr 49 to eliminate monomer bivalency, were compared. The chromatographic approach has been used in project 25,006 to study the dependence of hormone-mediated NP self-association on the intactness of the hormone binding surface. This method also is being used to study the nature of interactions of active site peptide ligands with polypeptide fragment complexes of the thermostable protease, thermolysis.